Yellow fever and travel vaccination

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

Yellow fever virus circulates between mosquitoes and non-human primates in forest cycles and can spread to humans through Aedes, Haemagogus or Sabethes vectors. Urban transmission occurs when viraemic humans infect competent mosquitoes. Endemic risk is geographically restricted but changes with outbreaks, vaccination coverage and travel regulations.

After cutaneous inoculation, virus replicates in lymphoid tissue and disseminates to liver, kidneys, myocardium and other organs. Mid-zonal hepatocellular injury, endothelial dysfunction, cytokine activation and coagulopathy produce jaundice, bleeding, shock and multiorgan failure. The absence of a licensed antiviral makes prevention and early physiological support central.

The live attenuated 17D vaccine is highly effective, but rare yellow-fever vaccine-associated neurotropic and viscerotropic disease can be severe. The decision therefore compares destination-specific disease risk and certificate rules with host-specific vaccine risk. A waiver addresses entry certification only; it does not protect the traveller from infection.

A good pre-travel consultation begins with dates, route, season, purpose, rural or urban setting, altitude, accommodation and activities. It then integrates age, pregnancy, immunity, comorbidity, medicines and prior vaccination. Recommendations should distinguish infection-risk protection from border requirements and remain feasible before departure.

Key points

Yellow fever is a mosquito-borne flavivirus transmitted in parts of sub-Saharan Africa and tropical South America through sylvatic, intermediate and urban cycles.
Initial illness causes abrupt fever, severe headache, myalgia, nausea, relative bradycardia and conjunctival injection; most patients then improve.
A minority enter a toxic phase after brief remission with recurrent fever, jaundice, bleeding, shock, kidney injury, myocarditis and encephalopathy.
First-line assessment includes malaria testing, FBC, coagulation, renal and liver profiles, glucose, lactate, blood cultures and organ-directed imaging while RIPL testing is arranged.
Reference RT-PCR is most useful during early viraemia; serology later can cross-react with other flaviviruses and vaccines and needs expert interpretation.
There is no proven specific antiviral treatment: use meticulous supportive care, haemodynamic and renal support, glucose management and cautious blood products.
Stamaril is a live attenuated vaccine given as one 0.5 mL dose at an approved Yellow Fever Vaccination Centre, ideally at least 10 days before exposure.
The International Certificate of Vaccination becomes valid 10 days after primary vaccination and remains valid for life for most travellers under the International Health Regulations.
Vaccination is not automatic when a certificate is requested; assess actual itinerary risk, entry rules, age, pregnancy, immunity, thymus history and serious-adverse-event risk, using a waiver when appropriate.
Travel health also includes routine immunisations, destination vaccines, malaria prevention, food and water safety, mosquito avoidance, sexual health, accident reduction and insurance.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Yellow fever virus

An enveloped flavivirus causes human disease after inoculation by infected mosquitoes in defined African and South American regions.

African vectors

Aedes mosquitoes maintain sylvatic, intermediate and urban transmission cycles involving non-human primates, forest workers and susceptible human populations.

South American vectors

Haemagogus and Sabethes mosquitoes drive forest transmission, with occupational and recreational forest exposure creating human cases.

Travel acquisition

Unvaccinated or incompletely protected travellers acquire infection through daytime mosquito bites, with risk shaped by place, season and outbreak activity.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Viraemic dissemination
Virus replicates in local lymphoid tissue and enters blood, reaching liver, kidneys, myocardium, spleen and other organs.
2
Hepatocellular injury
Mid-zonal apoptosis and inflammation impair hepatic function, producing jaundice, coagulopathy, hypoglycaemia and characteristic Councilman bodies histologically.
3
Endothelial and coagulation failure
Cytokine activation, endothelial dysfunction, thrombocytopenia and reduced clotting-factor synthesis combine to cause capillary leak and haemorrhage.
4
Multiorgan toxic phase
Renal tubular injury, myocardial dysfunction, shock and encephalopathy reinforce one another after the transient remission in severe cases.
5
Live-vaccine immunity
Attenuated 17D virus induces durable neutralising antibody and cellular immunity, while rare uncontrolled replication causes viscerotropic disease.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Acute febrile phaseRed flag

Abrupt fever, chills, severe headache, backache, myalgia, nausea, vomiting and conjunctival injection begin after a short incubation.

Relative bradycardia

Pulse may rise less than expected for the temperature, but this non-specific Faget sign cannot establish diagnosis.

Brief remission

Fever and symptoms may improve after several days; most recover, while severe cases progress after hours of apparent improvement.

Toxic phaseRed flag

Recurrent fever with jaundice, epigastric pain, haematemesis, mucosal bleeding, oliguria, shock or encephalopathy marks severe visceral disease.

Vaccine-associated neurotropic diseaseRed flag

Fever followed by meningitis, encephalitis, acute disseminated encephalomyelitis or Guillain–Barré-like weakness occurs rarely after vaccination.

Vaccine-associated viscerotropic diseaseRed flag

Post-vaccine fever progresses to hypotension, hepatitis, renal or respiratory failure and resembles wild-type severe yellow fever.

Red flags requiring action

Jaundice, haematemesis, melaena, mucosal bleeding, oliguria, hypotension or confusion after a compatible journey indicates toxic-phase yellow fever.
A brief remission followed by recurrent fever and organ dysfunction is characteristic of progression rather than recovery.
Any febrile traveller from a malaria-risk area still needs urgent malaria microscopy or rapid testing irrespective of yellow-fever vaccination history.
Severe allergy, significant immunosuppression, thymus disease, age under six months or previous serious yellow-fever vaccine reaction is a contraindication to live vaccine.
Age 60 years or older, pregnancy, breastfeeding, age six to eight months and selected immune conditions require individual specialist benefit-risk assessment.
New fever with jaundice or neurological illness soon after vaccination may represent vaccine-associated viscerotropic or neurotropic disease and needs urgent expert review.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
Immediate malaria testingFirst step
Why
Exclude a common, rapidly fatal and treatable cause of fever after travel.
Interpretation and limitations
Send urgent thick and thin films or validated rapid testing and repeat according to the malaria pathway when initial tests are negative but suspicion remains.
02
First-line severity panelFirst line
Why
Quantify hepatic, renal, haematological and metabolic injury and guide organ support.
Interpretation and limitations
Request FBC, coagulation, glucose, electrolytes, creatinine, bilirubin, AST, ALT, lactate, blood gas and urinalysis; thrombocytopenia, coagulopathy and rising creatinine indicate severe disease.
03
RIPL yellow-fever RT-PCR
Why
Directly detect viral RNA during early viraemia and distinguish wild-type infection from competing febrile illnesses.
Interpretation and limitations
Contact RIPL before sampling, provide onset, itinerary and vaccine dates, and send the recommended blood or tissue specimens using the advised pathway.
04
Yellow-fever serology
Why
Support diagnosis after viraemia wanes or when PCR is negative later in illness.
Interpretation and limitations
Flavivirus cross-reaction and recent vaccination complicate IgM and neutralisation results; paired samples and reference interpretation may be required.
05
Broader imported-fever testing
Why
Identify dengue, viral hepatitis, leptospirosis, enteric fever or another treatable infection.
Interpretation and limitations
Select blood cultures, arbovirus PCR or serology, hepatitis markers and zoonotic testing from exact geography, exposure and illness day.
06
Organ-directed assessment
Why
Guide management of shock, bleeding, myocarditis, renal failure and encephalopathy.
Interpretation and limitations
Use ECG, troponin, echocardiography, chest imaging, frequent glucose, neurological observation and renal monitoring according to physiology.
07
Pre-vaccination clinical assessment
Why
Determine whether live vaccine is indicated, contraindicated or needs expert risk balancing.
Interpretation and limitations
Verify itinerary and certificate rule, age, pregnancy, breastfeeding, allergy, thymus history, immune state, medicines and prior vaccine documentation before administering.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Severe malaria

Fever, jaundice, shock and renal failure overlap, making urgent repeated blood-film testing essential even after yellow-fever vaccination.

Dengue

Fever, thrombocytopenia, capillary leak and bleeding overlap; geography, illness timing and arboviral PCR or serology distinguish them.

Leptospirosis

Freshwater or animal exposure, calf myalgia, conjunctival suffusion, jaundice and renal injury suggest leptospiral Weil disease.

Viral hepatitis

Hepatitis A, B or E can cause fever and jaundice, usually without the same haemorrhagic shock pattern.

Other haemorrhagic fever

Ebola, Marburg, Lassa and Crimean-Congo haemorrhagic fever require immediate high-consequence infection risk assessment from exact epidemiology.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01ILL TRAVELLERStabilise and test in parallelFirst stepFever, jaundice or haemorrhagic features follow travel in a yellow-fever risk area.

1Use ABCDE, isolate from mosquitoes, obtain the severity panel and urgent malaria films, and manage hypoglycaemia, shock, bleeding and organ failure immediately.
2Contact infection specialists, the local health-protection team and RIPL before reference sampling; provide precise countries, dates, mosquito exposure and vaccination history.
3Send time-appropriate PCR and serology plus competing imported-fever tests, while avoiding aspirin, NSAIDs and unnecessary intramuscular injections when bleeding risk is present.
4Notify suspected yellow fever without waiting for confirmation and involve critical care, renal, hepatology and haematology services according to organ injury.

02ITINERARYBuild the travel risk profileA traveller requests vaccination or advice before an international journey.

1Map every country, transit, border crossing, date, season, rural or urban setting, altitude, accommodation, activity, animal contact and healthcare plan.
2Check authoritative NaTHNaC country guidance for yellow-fever disease risk and entry certificate rules; these are related but not identical questions.
3Review routine vaccines, destination-specific vaccines, malaria chemoprophylaxis, mosquito and tick prevention, food and water, sexual health, accidents and travel insurance.
4Prioritise interventions by likelihood, severity, time to departure and feasibility, documenting advice and any declined recommendation.

03VACCINATEGive vaccine safely when benefit exceeds riskThe itinerary presents meaningful yellow-fever risk or a justified certificate requirement and no contraindication is present.

1Verify identity, informed consent, contraindication screen and prior certificate, then give one 0.5 mL Stamaril dose at an approved Yellow Fever Vaccination Centre.
2Schedule primary vaccination at least 10 days before arrival or certificate use; explain that international validity begins on day 10, not immediately.
3Issue and complete the International Certificate accurately; a valid primary certificate generally remains valid for life under International Health Regulations.
4Explain expected fever or local reactions and urgent symptoms of neurotropic or viscerotropic disease, and reinforce mosquito protection despite vaccination.

04DEFER OR WAIVEManage contraindication or disproportionate vaccine riskLive vaccine is contraindicated or host risk may exceed benefit for the planned itinerary.

1Do not vaccinate after severe component allergy, significant immunosuppression, thymus disorder associated with immune dysfunction, age under six months or a previous serious vaccine reaction.
2For age 60 or older, pregnancy, breastfeeding, age six to eight months or selected immune conditions, obtain expert benefit-risk assessment using exact destination and exposure probability.
3When travel is avoidable, alter route, timing or destination; when only a certificate issue remains and vaccination is inappropriate, issue a medical waiver from an authorised centre.
4Explain that a waiver may not be accepted at every border and provides no biological protection, so intensive daytime mosquito precautions remain essential.

05COADMINISTERPlan other vaccines and timingYellow-fever vaccine is needed alongside routine or travel vaccines.

1Give most inactivated vaccines at any interval and use separate sites; check each product and current Green Book advice rather than applying a single spacing rule.
2Give yellow-fever and MMR vaccines four weeks apart where feasible because simultaneous administration may reduce immune responses to some antigens.
3When urgent travel prevents spacing, vaccines may be given at any interval after informed specialist assessment, with additional doses considered according to current guidance.
4Review oral live vaccines, immune globulins and immunosuppressive medicines individually, and record the rationale for any altered schedule.

Key medicines and prescribing safety3 treatments · regimens, roles and cautions

First-line prevention for travellers with meaningful destination risk when benefits exceed live-vaccine harms, and the only vaccine that supports an International Certificate of Vaccination.

Yellow-fever 17D vaccine (Stamaril)

Give one 0.5 mL dose by the licensed subcutaneous route, or intramuscular route where appropriate under official recommendations, at an approved Yellow Fever Vaccination Centre.

Screen severe egg or component allergy, immune suppression, thymus disease, pregnancy, breastfeeding and age; use only trained authorised-centre processes and never vaccinate solely to satisfy paperwork when risk is disproportionate.

Symptomatic relief for fever and pain during uncomplicated illness or expected post-vaccine reactions.

Paracetamol

Use standard adult oral or intravenous dosing within the product maximum, reducing or avoiding it when severe hepatic dysfunction makes usual dosing unsafe.

Do not exceed combined-product limits; severe yellow-fever hepatitis requires senior pharmacy or hepatology review, and symptom control must not delay reassessment of deterioration.

Supportive treatment for capillary leak, shock, haemorrhage and organ dysfunction because no proven antiviral therapy exists.

Intravenous fluids and blood components

Titrate balanced crystalloid in small reassessed boluses to perfusion, urine output and lactate; give blood components for clinically significant bleeding or laboratory-guided coagulopathy.

Avoid fluid overload in renal, myocardial or capillary-leak disease, use critical-care haemodynamic assessment, and do not correct abnormal coagulation tests with blood products in the absence of bleeding or a planned procedure.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Fulminant hepatic failure

Severe hepatocyte injury causes jaundice, coagulopathy, hypoglycaemia, encephalopathy and impaired clearance of medicines, ammonia and circulating lactate.

Haemorrhage

Thrombocytopenia, endothelial injury and reduced clotting factors produce gastrointestinal, mucosal, pulmonary, urinary or puncture-site bleeding with haemodynamic consequences.

Acute kidney injury

Tubular injury, shock and haemolysis can cause oliguria, electrolyte disturbance, acidosis and need for renal replacement therapy.

Shock and myocarditis

Capillary leak, vasodilatation, bleeding and myocardial injury combine to cause refractory circulatory collapse, tissue hypoperfusion, acidosis and dangerous arrhythmia.

Vaccine-associated severe disease

Rare neurotropic or viscerotropic adverse events cause encephalitis, paralysis or multiorgan failure and require urgent specialist investigation.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

In severe disease, monitor blood pressure, perfusion, lactate, glucose, mental state, oxygenation, urine output, FBC, coagulation, renal and liver profiles frequently enough to detect rapid toxic-phase deterioration.
Reassess after every fluid or blood-product intervention because capillary leak, myocardial injury, kidney failure and bleeding create narrow physiological margins.
Maintain mosquito precautions during viraemia to prevent onward vector transmission where competent mosquitoes could be present, following health-protection advice.
After vaccination, give written advice on expected local pain or mild fever and urgent review for progressive fever, jaundice, dyspnoea, confusion, meningism or weakness.
Report suspected serious vaccine reactions through clinical and pharmacovigilance routes and coordinate RIPL testing to distinguish vaccine-associated from wild-type disease.
Check the certificate for correct name, date, vaccine, batch, signature and authorised-centre stamp before the traveller leaves.
Revisit the travel plan when route, health, pregnancy status, medicines or outbreak information changes before departure.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

Risk and requirement differ

A country may demand a certificate because of importation risk even when the traveller's itinerary has little exposure to yellow fever.

Day ten matters

Primary certificate validity and protective immune response are not immediate, so late attendance can change both entry and clinical advice.

A waiver is administrative

Medical exemption may address a border rule but cannot prevent infection and may still be rejected by national authorities.

One dose usually lasts

International certificate validity is lifelong for most people, although selected high-risk hosts or ongoing exposures need specialist booster assessment.

Vaccination does not exclude disease

Documentation may be inaccurate, immunity may be impaired and other severe imported infections remain possible in every febrile traveller.

Scope boundary

Yellow-fever disease and vaccine decisions are developed here; malaria, rabies, gastrointestinal, sexual-health and accident prevention retain their own pathways.

11Common pitfallsFrequent interpretation and management errors.

01
Do not interpret a yellow-fever certificate as proof that malaria, dengue, hepatitis or another imported infection is absent.
02
Do not give live yellow-fever vaccine without checking immunosuppression, thymus history, pregnancy, breastfeeding, age and severe allergy.
03
Do not vaccinate an older low-risk traveller automatically for paperwork; compare actual disease exposure with serious vaccine adverse-event risk.
04
Do not promise that a primary certificate is valid immediately; it begins 10 days after vaccination.
05
Do not describe a medical waiver as protection or guarantee its acceptance by border authorities.
06
Do not use aspirin or NSAIDs casually in suspected yellow fever or another haemorrhagic arboviral illness.
07
Do not allow a destination vaccine checklist to displace malaria prevention, routine vaccination, food and water, sexual safety, accidents and insurance.